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From: Bill Paul <wpaul@FreeBSD.org>
Date: Sat, 26 Feb 2005 00:22:16 +0000 (UTC)
To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org,
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X-FreeBSD-CVS-Branch: HEAD
Subject: cvs commit: src/sys/compat/ndis kern_ndis.c ntoskrnl_var.h
 subr_ntoskrnl.c
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wpaul       2005-02-26 00:22:16 UTC

  FreeBSD src repository

  Modified files:
    sys/compat/ndis      kern_ndis.c ntoskrnl_var.h 
                         subr_ntoskrnl.c 
  Log:
  MDLs are supposed to be variable size (they include an array of pages
  that describe a buffer of variable size). The problem is, allocating
  MDLs off the heap is slow, and it can happen that drivers will allocate
  lots and lots of lots of MDLs as they run.
  
  As a compromise, we now do the following: we pre-allocate a zone for
  MDLs big enough to describe any buffer with 16 or less pages. If
  IoAllocateMdl() needs a MDL for a buffer with 16 or less pages, we'll
  allocate it from the zone. Otherwise, we allocate it from the heap.
  MDLs allocate from the zone have a flag set in their mdl_flags field.
  When the MDL is released, IoMdlFree() will uma_zfree() the MDL if
  it has the MDL_ZONE_ALLOCED flag set, otherwise it will release it
  to the heap.
  
  The assumption is that 16 pages is a "big number" and we will rarely
  need MDLs larger than that.
  
  - Moved the ndis_buffer zone to subr_ntoskrnl.c from kern_ndis.c
    and named it mdl_zone.
  
  - Modified IoAllocateMdl() and IoFreeMdl() to use uma_zalloc() and
    uma_zfree() if necessary.
  
  - Made ndis_mtop() use IoAllocateMdl() instead of calling uma_zalloc()
    directly.
  
  Inspired by: discussion with Giridhar Pemmasani
  
  Revision  Changes    Path
  1.68      +2 -15     src/sys/compat/ndis/kern_ndis.c
  1.29      +4 -0      src/sys/compat/ndis/ntoskrnl_var.h
  1.56      +41 -3     src/sys/compat/ndis/subr_ntoskrnl.c